To provide a ladder which eliminates an unstable state of the worker at the time of opening/closing operation on the ladder, and therefore is optimum for a foundation scaffolding for use in a construction site in which vertically moving and incoming/outgoing frequency is high.

Upper ends of right and left vertical poles 3 and 2 of the ladder 1 are upward extended to a location higher than a top face of a scaffolding board A2 of an entrance A1 of the ground scaffolding A, and a step A5 located at an uppermost location of the ladder 1 is set to a height lower than the top face of the scaffolding board A2 of the foundation scaffolding A, to thereby secure a spatial portion 4 communicating with the entrance A1, at a location above the ladder. The ladder includes an openable pole 5 for opening/closing an upper portion of the spatial portion 4 across the right and left vertical poles 3 and 2, in a manner being parallel with a handrail A3 of the foundation scaffolding A at a height at which it functions as the handrail on the scaffolding board A2. The openable pole 5 has one end thereof pivotally supported by one of the right and left vertical poles 3 and 2, and the other end thereof disengageably engaged with a receiving portion 6 on the other side of the right and left vertical poles 3 and 2, to thereby make openable the entrance A1 and an open portion 41 at the upper portion of the spatial portion 4.